In a temperature detection device of this type, a pull-up resistor is provided between a power supply voltage line and one end of a temperature sensor, the other end of which is connected to a ground line, thereby to develop at a junction between the resistor and the temperature sensor a sensor voltage, which corresponds to a resistance value of the temperature sensor and hence to a temperature of a detection object. The temperature detection device detects the sensor voltage and calculates the temperature of the detection object based on a detection value of the sensor voltage.
Further, according to a temperature detection device disclosed in JP-A-2009-250613, two series resistors are provided as pull-up a resistor and two output terminals of a transistor are connected to both ends of one resistor of the two series resistors provided at a power supply voltage line side. In this temperature detection device, the transistor is switched over to turn on and off to vary the resistance value of the pull-up resistor. Thus a temperature-voltage characteristic of the sensor voltage relative to temperature is switched over between a first temperature-voltage characteristic and second temperature-voltage characteristic. With this configuration, failure of the temperature sensor can be detected surely and accuracy of temperature detection can be improved.
According to the conventional temperature detection device, it is not assumed that the voltage developed between the output terminals of the transistor in the on-state varies with aging deterioration and temperature. For this reason, accuracy of temperature detection is lowered in a state that the transistor is in the on-state.